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Richard Smith, Georges A Goetz, Xin Lei, Theodore Kamins, James Harris, Keith Mathieson, Daniel V Palanker, Alexander Sher; Contrast sensitivity in photovoltaic prosthesis-activated degenerate retina. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3239.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the contrast sensitivity of the network-mediated responses of the retinal ganglion cells activated via subretinal photovoltaic prosthesis in degenerate rat retina, and compare it to the contrast sensitivity of natural light responses in healthy retina.
Photovoltaic arrays with pixel sizes of 70 and 140µm were placed on the photoreceptor side of normally-sighted (Long Evans, LE) and degenerate (p110-370, Royal College of Surgeons, RCS) rat retinas while network-mediated responses were recorded from the RGCs using a 512 channel multielectrode array. For prosthesis-mediated vision, full-field illumination was projected on the implant using 880nm wavelength, with pulse duration of 4ms and repetition rate of 20Hz, while its irradiance was changed every 500ms. Mean peak irradiance was kept constant at 2.5 or 5 mW/mm2 throughout the experiment. Contrast sensitivity of RGCs in the healthy retina was characterized using 500ms long visible light pulses, with the irradiance varying stochastically around a low photopic mean adaptation level.
With prosthetic vision, we observed electrical ON (59% of RGCs), electrical ON/OFF (27% of RGCs), and electrical OFF (14% of RGCs) responses to intensity steps in WT retina. RCS retina had fewer electrical OFF responses, with electrical ON responses comprising 89% of total RGCs. The majority (84%) of eON/OFF RGCs in WT retina were the ON-center cells, as classified by the responses to visible light white noise stimulus. Contrast sensitivity to visible light stimulation in healthy retinas was much higher than to the photovoltaic stimulation: RGCs responded to visible light changes with contrast as small as 1% in WT retina, while the prosthetic ON responses in RCS retina required, on average, changes with approximately 65-70% contrast. A subset of more sensitive cells responded to changes of 30% with 70µm pixels, and as low as 10% contrast with 140µm pixels.
We observed both eON and eON/OFF responses to contrast steps with prosthetic-mediated vision, with the OFF component of the response likely mediated by photoreceptors. Contrast sensitivity of prosthetic vision was much lower than that of normal vision, indicative that a contrast-enhancement pre-processing step will be required to deliver meaningful visual information to a patient.
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